Bayesian mixture analysis. a) Individual-based mixture analysis of 1225 Galápagos marine iguanas to 20 genetic clusters as determined by the program STRUCTURE following the estimation of true number of genetic clusters (K) following  Evanno et al. (2005; see Figure S1 [see Additional file 5]). Note that individual samples taken at two different time points (i.e. in 1991/93 and 2004) on an island location represent the same genetic cluster. With the exception of Fernandina and Isabela all major islands each represent a distinct genetic cluster. b) Population-based mixture analysis for the same number of genetic clusters according to STRUCTURE. For (a) and (b) the program DISTRUCT  (Rosenberg 2004) was used to generate the display genetic clusters and degree of admixture of individuals.